Effects of different glucose concentrations on spinal anaesthesia with bupivacaine and tetracaine

The effects of 5% and 8% glucose in 0.5% tetracaine or bupivacaine on the anaesthetic spread were investigated in 80 urological patients requiring spinal anaesthesia for trans-urethral resection of the prostate. The local anaesthetic solutions were randomly administered, the patients being divided into four groups of 20, and the anaesthetic profile was then evaluated in a double-blind fashion by an independent observer. Maximum cephalad spread of analgesia was significantly greater with tetracaine in 8% glucose compared to the other three groups (tetracaine/5% glucose, bupivacaine/5 or 8% glucose) (P less than 0.05). Glucose concentration significantly influenced spreading characteristics of tetracaine, the 8% solution achieving a higher level in a shorter time than the 5% solution. Sensory regression to both T10 and S1 dermatome was longer with bupivacaine in 8% glucose compared to 5% glucose. The concentration of glucose, however, did not influence the regression of sensory analgesia for tetracaine. Both the 5% and 8% solutions of tetracaine achieved a 3+ motor blockade significantly faster than either bupivacaine solution. Regression of motor blockade from tetracaine was not influenced by the glucose concentration, but the 8% solution of bupivacaine had a delayed 2+ and 3+ blockade, although the ultimate decay for both solutions was similar. The results of our study suggest that 0.5% bupivacaine 4 ml in 5% glucose provides a rapid and controllable spread of sensory analgesia for transurethral surgery, of optimal duration associated with a complete motor blockade of moderate duration.